Soft wall hydrometer

ABSTRACT

A specific gravity-sensing instrument in which a closed cell having highly compliant walls is completely filled with a reference liquid and immersed in an ambient liquid, and compensation is made for the difference in compression and thermal expansion of the material comprising the cell walls with either the reference liquid or ambient liquid so that when the cell is immersed, it responds equally to changes in density of the reference liquid and ambient liquid, thereby cancelling the effects of pressure and temperature and so as to measure directly the changes in specific gravity.

United States Patent [72] Inventor Homer S. Youngs 2,094,768 10/1937Cruse et a] 73/451 8718 Dunaway Dr.. La Jolla, Calif. 92037 2,282,069 5/l 942 Linebarger. 73/454 [21] Appl. No. 868,564 3,137,158 6/1964 Krueger73/30 F11d 0C. 22. 1969 FOREIGN PATENTS [45] Patented Sept. 14, 197icontinuafianmpafl of application Sen No. 734,684 10/ 1932 France 73/449583,244, Nov. 30, 1966, now abandoned. OTHER REFERENCES Long OceanSciences" 1965, page 141 (copy enclosed) Primary Examiner-Richard C.Quiesser Assistant Examiner-Ellis J. Koch 54 1 SOFT WALL HYDROMETER 5Claims, 21 Drawing Figs.

[52] U.S. Cl 73/449,

73/30' 73/170, 73/454 ABSTRACT: A specific gravity-sensing instrument inwhich a [51] Int. Cl G0ln 9/08, dosed Ce having highly compliant wallsis completely fill d 9/12 with a reference liquid and immersed in anambient liquid, and [50] Fleld of Search 73/32, 437, compensation i madef the difference i compression and 450,451, 452,453,454,444, 448, 449,170. 30 thermal expansion of the material comprising the cell walls 1 56 R f C1 ed with either the reference liquid or ambient liquid so thatwhen 1 l e erences I the cell is immersed, it responds equally tochanges in density UNITED STATES PATENTS of the reference liquid andambient liquid, thereby cancelling 794,697 7/1905 Beck et al, 73/449 theeffects of pressure and temperature and so as to measure 2,000,3085/1935 Van Shutz 73/30 directly the changes in specific gravity.

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PATENTED SEP] 4197 3604.272

sum 1 or 4 I N VENTOR. 1 /0415 5. You/v65 rrake/vf ys SOFT WALLll-IYDROMIETIEIR The present invention is a continuation in part of mycopending application, Ser. No. 583,244, filed Sept. 30, 1966, nowabandoned entitled Soft Wall Hydrometer.

SUMMARY OF THE INVENTION This invention relates to soft wallhydrometers; more particularly to a hydrometer which is distinguishedfrom previous hydrometers or similar instruments by the fact that thewalls which separate the reference fluid from the surrounding fluid arehighlycompliant so that the reference fluid is maintained at the samepressure as the surrounding fluid or varies without hysteresis effect inaccordance with change in pressure of the surrounding fluid.

Included in the objects of this invention are:

First, to provide a soft wall hydrometer which facilitates theperforming of specific gravity measurements under extreme pressures,without sacrifice of precise measurement, and which in fact permits moreaccurate measurement than has heretofor been feasible or possible exceptunder accurately controlled laboratory conditions.

Second, to provide a soft wall hydrometer which is capable of accuratespecific gravity measurement without special thermal control, inasmuchas the necessarily thin and compliant wall offers no appreciableresistance to the transfer of heat between the contained reference fluidand the surrounding or ambient fluid.

Third, to provide a soft wall hydrometer which, although ideally suitedfor laboratory use, is capable of accurate measurement even underadverse conditions; such as encountered at great depths in the ocean, orthose encountered in the continuous or periodic measurement of fluidsundergoing treatment in a processing plant or flow in a pipeline.

. Fourth, to provide a hydrometer in which error due to bubble formationis minimized.

Fifth, to provide a hydrometer which facilitates the measurement ofhighly volatile or inflammable liquids or gases.

Sixth, to provide a soft wall hydrometer which is adaptable to variousforms or types corresponding to those of conventional hydrometers; suchas, totally immersed angular or linear balances of the float and weight,multiple float, spring-opposed types, whether the direct reading or nullbalance types; and as well as various forms of emergent stemhydrometers.

Seventh, to provide a soft wall hydrometer wherein the reference liquidmay be a particular sample of the surrounding or ambient liquid; forexample, in the measurement of sea water at various depths.

Eighth, to provide a soft wall hydrometer with auxiliary counterbalanceelements whose functions include net instrumental compressibility andthermal expansivity matching to the reference fluid contained within thesoft wall cell.

DESCRIPTION OF THE FIGURES FIG. 1 is a side view, showing a pair ofsupporting structures for soft wall hydrometers, adapted particularlyfor oceanographic studies, the uppermost structure being shown asundergoing a cycle of operation in which the hydrometer is released soas to make a record of the specific gravity of the sea water, whereasthe lower structure is shown in the condition prior to its operatingcycle.

FIG. 2 is an enlarged fragmentary side view, taken within circle 2ofFIG. 1.

FIG. 3 is a similar fragmentary side view, taken within circle 3 of FIG.1.

FIG. 4 is an enlarged fragmentary view of the housing structure, withportions broken away to show the hydrometer and its associatedmechanism.

FIG. 5 is a fragmentary sectional view, taken through 5-5 of FIG. 4,showing a window for the admission of sea water, in its open condition.

FIG. 6 is a similar view, showing the window in its closed condition.

FIG. 7 is a fragmentary sectional view, taken through 7-7 of FIG. 4,showing the clutch spring and the clutch-tensioning cam.

FIG. 8 is an essentially diagrammatical perspective view, showing theelectrical relationship between the soft wall hydrometer unit and thescale associated therewith.

FIG. 9 is a further enlarged transverse sectional view, taken through9-9 of FIG. 4, showing the soft wall hydrometer and the scale-supportingstructure in their locked condition.

FIG. 10 is a fragmentary sectional view, taken through 10- 10 of FIG. 4,showing the manually operated stop employed to terminate the cycle ofoperation.

FIG. II is a fragmentary sectional view, taken through ill- II of FIG.4, showing the electrode pointer and adjacent portion of the scale.

FIG. 12 is a fragmentary sectional view, taken within circle 12 of FIG.9, showing the clutch in its released condition, wherein the soft wallhydrometer is free to make a record of the specific gravity of thesurrounding sea water.

FIG. 23 is an essentially diagrammatical view, illustrating a modifiedform of the hydrometer, in which the hydrometer is suspended in theambient liquid and is equipped with a stem projecting into a companionliquid. The location of the stem, with respect to the interface betweenthe ambient fluid and the companion fluid, being indicative of thespecific gravity of 4 the companion fluid or the ambient fluid,depending upon which fluid is treated as a variable.

FIG. 14 is a similar essentially diagrammatical view, in which thehydrometer is inverted with respect to the position shown in FIG. 13,for use in conditions in which the companion fluid has a greater densitythan the ambient fluid.

FIG. I5 is a fragmentary view, showing a further modification of thesoft wall hydrometer, immersed in an ambient fluid, and connected to acounterweight chain or flexible linkage, which in turn is connected to ameans for vertically adjusting the linkage to facilitate reading of thespecific gravity of the ambient liquid.

FIG. I6 is an enlarged fragmentary sectional view, taken within circle116 of FIG. 15.

FIG. 17 is an enlarged fragmentary sectional view, taken within circle17 of FIG. I5.

FIG. 18 is an exploded view, showing the parts of a further modifiedsoft wall hydrometer.

FIG. 19 is an enlarged fragmentary sectional view, taken within circle19 of FIG. I8.

FIG. 20 is a reduced side view of the soft wall hydrometer, shown inFIGS. 18 and I9, and illustrating one manner of its use.

FIG. 21 is an essentially diagrammatical perspective view, illustratinga further modified form of the soft wall hydrometer.

Reference is first directed to FIGS. 1 through 12, which illustrate indetail one embodiment of the invention, especially arranged foroceanographic surveys. In the exercise of this form of the invention,housing structures, each containing a soft wall hydrometer, are mountedon a suspension line I, so that specific gravity readings may beobtained at different levels. Each supporting structure includes a frame2, having a sleeve 3, through which the line 1 extends. Suitable means,not shown, are employed to secure each sleeve to the line and to allowfree rotation of the frame 2 about the sleeve 3 as an axis, to align theframe 2 with possible water currents.

At one side of the sleeve 3, the frame incorporates a counterbalance andbattery power supply housing 4. Connected to the other side of the frame2, is a hydrometer housing 5. The hydrometer housing 5 includes acircular rim 6, to which are secured opposed sidewalls 7 and 8 in theform of convex disks.

A fixed journal shaft 9 is secured in the sidewall 7 and extends alongthe axis defined by the rim 6 and through the sidewall 8. Mounted on theshaft 9 is an insulating sleeve 10, which is restrained againstrotation. Journaled on the sleeve 10 is a conductor collar II which inturn journals a fulcrum hub 12, which is located intermediate the ends.of a pivot member 13. One arm 14, of the pivot member, is connected bya bracket 15, secured by an adjustment screw 16, to a soft wallhydrometer cell 17.

The soft wall hydrometer cell constitutes the crux of this invention. Byreason of the soft wall hydrometer cell, specific gravity measurementsof extremely high accuracy may be made.

The soft wall hydrometer cell is a liquid container, having extremelythin or at least highly compliant walls 18. The cell may be in the formof a hollow disk, having circular flat sides. The walls may be formed ofplastic material or of thin-gauge metal. In the latter caseparticularly, the sidewalls may be corrugated so that any resistance topressure differential across the wall is minimized. It is essential tothe operation of the soft wall hydrometer that the chamber formed by thewalls be completely filled with a reference liquid 19.

The pivot member 13 includes a second arm 20, on which is mounted aradially adjustable counterbalance 21. The arm terminates in a pointeror marker electrode 22, in the form of a wire offset from the plane ofthe arm 20, and extending radially, as shown in FIGS. 4, 8 and 11.

The sensitivity of the angular soft wall hydrometer is determined by theangular displacement, about the axis 9, of the centers of buoyancy andof gravity of the rotational unit, including items 12 to 22 inclusive.This adjustment is achieved by positioning the counterbalance 21 alongthe arm 20 and by angularly positioning the cell 17 with respect to thearm 14 by means of the adjustment screw 16 and the bracket 15.

In the construction illustrated, the reference liquid 19 has a specificgravity greater than the liquid in which the hydrometer cell isimmersed. For example, in this case, if the hydrometer cell is immersedin sea water, the reference liquid would have a specific gravity greaterthan sea water; however, its compressibility would correspond to that ofsea water. Consequently, the hydrometer cell tends to rotate therotational unit counterclockwise, as viewed in FIG. 4, and thecounterbalance 21 is a weight.

Should it be desirable to use a reference liquid 19 which has lessspecific gravity than the ambient liquid, so that the cell 17 would tendto rotate the rotational unit in a clockwise direction, thecounterbalance 21 would also be buoyant or, if needed, located on thearm 14. In this case, it would be preferred to position the cell 17above the pivot member 16.

Also rotatably mounted on the shaft 9 is a scale support 23, having ahub 24. The scale support includes an arcuate rim 25, occupying aboutone-third of a circle. Occupying a portion of the rim 25, is an arcuatescale 26, removably secured by screw attachments 27. The rim 25 alsosupports a counterweight 28. In order to provide access to the scale,the sidewall 7 is provided with a removable cover 29.

The rim 6 is provided internally with a set of recesses which receiveflanged journaling rollers 30. The rollers rotatably support a timingring 31. On the axial side of the timing ring 31, facing the sidewall 7,is a ring gear 31a. 1

Supported from the upper portion of the frame 2, and also supported fromthe periphery of the hydrometer housing 5, is a motor housing 32, whichcontains a spring-operated drive motor 33, which includes a drive pinion34, adapted to engage the ring gear 31a.

Secured to the axial side of the timing ring 31, facing the sidewall 8,is a disk 35, conforming to the curvature of the sidewall 8. The disk 35is provided with a pair of relatively large diametrically disposedopenings 36, which in the course of operation of the hydrometer, arecaused to register with similar openings 37, provided in the sidewall 8.It is intended that the timing ring 31 and its disk 35 make one-halfrevolution in the course of operation of the hydrometer. In order to dothis, a marker control pin 38, which may be one of the screws connectingthe disk 35 to the timing ring 31, protrudes axially toward the sidewall7.

A manually releasable stop 39 is provided, as shown in FIGS. 4 and 10.This manual stop is released at the time the soft wall hydrometer iscocked and prepared for use, as will become hereinafter evident. In thecourse of rotation of the timing ring 31, the pin 38 engages a switch40, mounted in the sidewall 7, which completes a circuit through themarker electrode 22, scale 26 and scale support 23, as will be broughtout hereinafter.

Bordering the radially inner sides of the openings 36, is a pair of camflanges 41, illustrated in FIGS. 4, 7 and 9. A leaf spring 42 bridgesbetween the cam flanges 41 and is mounted on the shaft 9 by means of aclutch collar 43. Theclutch collar is a square in cross section, andfits within a square opening provided at the center of the sidewall 8,so as to slide axially, but be restrained against rotation.

The journal shaft 9 protrudes through the sidewall 8, and is capped by aguide sleeve 44. A spring 45, which is weaker than the leaf spring 42,extends between the sidewalls 8 and the outer extremity of the guidesleeve 44. When the extremities of the leaf spring 42 are engaged withthe crest of the cam flanges 44, as shown in FIG. 9, the clutch collar43 is urged axially against the hub 24 of the scale support 23. The hub24 in turn presses against a washer 46, of insulating material, which inturn presses against the hub 12 of the pivot member 13, so that thehydrometer and its scale are locked against rotation. When the leafspring 42 is free of the cam flanges 41, the

clutch collar 43 releases the hydrometer and its scale, as indicated inFIG. 12.

Included in the spring motor 33, is a gear having vanes 47, which,inasmuch as the spring motor is immersed in water during its operation,may serve as a governor. One of the vanes is initially engaged by alatch pin 48, mounted on a slide bar 49. The latch bar is verticallymovable through the motor housing. The latch pin is guided in a slot 50,provided in the motor housing. A second pin and slot means51 limits theslide bar 49 to axial movement, as shown in FIGS. 2 and 3. The slide bar49 extends below the housing 32 and is connected to a rod 52, guided bythe frame 2, and provided with a spring 53 so that normally the slidebar 49 occupies an upper position, shown in FIG. 2.

The upper extremity of the slide bar 49 extends above the motor housing32, and is attached to a lever 54, one end of which is pivotallyconnected to a bracket 55, extending from the rim 6. The other extremityof the bracket 55 is connected to a link 56 which in turn is connectedto a target disk 57, which surrounds the suspension line I. In order toinitiate operation of the hydrometer, a messenger 58 is released from apoint on the line above the hydrometer and caused to engage the targetdisk 57, so as to move the slide bar 49 from the position shown in FIG.2 to the position shown in FIG. 3. For this purpose, each messenger 58is provided with a retainer strap 59.

It is intended that a series of hydrometers be mounted on the suspensionline, and that each hydrometer, except the lowermost hydrometer,initially support a messenger, which will be released when the operationof the hydrometer is initiated. Operation of the uppermost hydrometer isinitiated by a messenger released from the ship from which the line 1 issuspended.

Each motor 33 includes a drive spring 33a mounted on a shaft 33bjournaled between the two plates forming the motor housing 32. The drivespring tends to rotate the shaft 33b in one direction and drive thegears of the motor in the opposite direction. Each motor housing 32 isprovided with a pair of arcuate slots 60, concentric with the shaft 33b.Secured to the shaft is a latch disk 61.

The latch disk is provided with a strap receiving notch 62, whichseparates two projections 63 and 64 in angular relation. Edge surfacesof the projections 63 and 64 confront the slide bar 49, and are soarranged that when the slide bar is in its upper position, shown in FIG.2, the latch disk is prevented from rotation, but when the slide bar 49moves downwardly, from the position shown in FIG. 2, to the positionshown in FIG. 3, the latch disk is driven counterclockwise to releasethe retainer strap 59, whereupon the latch disk is locked againstfurther rotation so that the drive spring may drive the pinion gear 34.

Operation of the hydrometer, shown in FIGS. 1 through 12, is as follows:

A series of hydrometers are secured to the suspension line 1, atappropriate intervals. In the conducting of an oceanographic survey, thesuspension line may extend to great depths. This has no adverse effecton the hydrometers or the component parts, as all elements may beexposed to the submergence pressure; that is, they need not be containedin pressure-resistant housings. This is true of the batteries, whichthough forming no part of the present invention, are arranged so thattheir contents are protected from or subjected to submergence pressures.

Prior to installation on the suspension line, each soft wall cell 17 iscompletely filled with a reference liquid 19 which may be, if desired,sea water or a selected reference liquid.

When the suspension line has been lowered so as to suspend the series ofhydrometers at the desired depths, a messenger, suitably retained at theupper end of the suspension line, is released and engages the targetdisk 57 of the uppermost hydrometer. This causes the slide bar 49 to bedepressed, as indicated in FIG. 3, releasing a second messenger toengage the target disk of the hydrometer located below. Downwardmovement of the slide bar releases the spring motor so as to cause thering gear 31a, timing ring 31, and disk 35 to rotate in a clockwisedirection, as viewed in FIG. 4. Normally the openings 36 and 37 are inregistry to effect free exchange of the sea water within the hydrometerand the ambient sea water outside the housing 5. Rotation of thediskcloses the openings so that external currents do not disturb thereading. It should be noted that even when the openings are out ofregistry, the housing need not be watertight.

When the openings 36 and 37 are closed, the initial rotation of the disk35 releases the spring 42, clears the cams 41 so that the pivot member13 and the scale support 23 are free to rotate. As a result, therelative gravitational effect on the hydrometer unit and the scale isconstant, irrespective of the angular position occupied by thesuspension line, or to the angular position of the housing by reason ofthe fact that the housing is free to rotate about the axis of the sleeve3.

The hydrometer unit assumes an angular position relative to the scalethat depends upon the relative specific gravity of the reference liquid19 and the ambient sea water. No compensation need be made fortemperature for a reference liquid 19 sufficiently similar to sea water,as the reference liquid is exposed to the same temperature as theambient sea water. Also, the effect of submergence pressure is cancelledby reason of the fact that the reference liquid is subjected toprecisely the same pressure as the ambient sea water. As a result, theangular position of the hydrometer unit is dependent upon the specificgravity of the ambient sea water, due to factors other than submergencepressure and temperature.

In order to make a record of the angular position of the hydrometer, theswitch is momentarily closed by the pin 38 so that the current is causedto flow between the marker electrode 22 and the scale support 23,through the scale 26. It has been found feasible to form the scale frompaper or similar fibrous material, which has been impregnated with achemical sensitive to the passage of electric current therethrough, orto the occurrence of minute quantities of electrolytic products in thevicinity of the locations of closest approach of marker electrode 22 andscale 26 at the time of current flow. An example of such material isconventional blueprint paper, which has been previously exposed to lightand subsequently developed by water washing. The marker electrode neednot contact the paper so that frictional resistance to movement iseliminated. Nevertheless, a momentary current will cause a white mark toappear on the blueprint paper. While blueprint paper is suggested, itshould be understood that other suitable electrosensitive materials maybe used.

After the record has been made, the disk 35 continues to rotate tocomplete a half turn; that is, until the pin 38 engages the stop 39. Inthis final position of the disk 35, the leaf spring 42 has reengaged thecam flanges 41, relocking the hydrometer unit and the scale support, andthe openings 36 and 37 are in registry, to allow free communication ofthe ambient sea water with that within the hydrometer housing. Thehydrometer is now in locked condition, ready for return to the surfaceby raising the suspension line 1.

While a messenger system is illustrated, other means of operating aseries of hydrometers in sequence or simultaneously may be employed.Also, it should be noted that the suspension line may also carry othertypes of instruments interposed between the hydrometers, depending onthe requirements of the oceanographic survey.

The previously described structure illustrated an application of thesoft wall hydrometer to the conducting of oceanographic surveys.However, the soft wall hydrometer has many other applications, such asthe manual or automatic measurement of specific gravity of liquids inpipelines and various liquid processing plants, where well-known remotereporting or telemetering systems may be used cooperating with angularor linear forms of the soft wall hydrometer, as convenient. The softwall hydrometer is also adapted to laboratory use for the accuratemeasurement of specific gravity.

FIGS. 13 to 21 illustrate in essentially diagrammatical form, variousother modifications of the soft wall hydrometer.

Reference is first directed to FIG. 13, which illustrates an emergentstem type of my soft wall hydrometer. The hydrometer here illustrated,includes a soft wall cell 71. The walls of the cell may be formed ofyieldable plastic material or formed of metal. In the latter case, theconfiguration being such that the metal offers minimum resistance to thedeflection. The cell is completely filled with a reference liquid 72. Astem 73 extends from one end ofthe cell. In FIG. 13, the stem is shownas directed upwardly. Suitably supported over the stem 73, and a portionof the cell 71, is an inverted container 74, connected intermediate itsends to a supply line 75. The container and cell are immersed in anambient liquid 76, and the upper portion of the container is filled witha comparison liquid 77, of lower density than the ambient liquid. Thefluids 76 and 77 are selected so as to be immiscible and thereforedefine an interface 78 therebetween. Specific gravity may be measuredoptically by use of a reference mark 79 on the stem. Movement of themark may be noted, if the interface 78 is maintained constant, or theinterface may be raised or lowered by adding or subtracting comparisonfluid through the line 75, so as to maintain the reference mark at auniform height.

Reference is now directed to FIG. 14. In this case, the stem 73 isdirected downward and the cell 71 and its stem are positioned in anupright container 80. In this case, the comparison fluid 81 has higherdensity than the ambient liquid 76, and preferably the reference fluid82 has a density equal to or less than the ambient liquid. The positionof the hydrometer may be detected in the same manner as that indicatedin connection with FIG. 13. Alternatively, the stem 73 may contain anarmature 83 and its sensing coils 84 may be immersed in the comparisonliquid or surrounding the container 80.

Reference is now directed to FIG. 15. In this embodiment a soft wallcell 85 is illustrated, which as in the previous constructions is highlycompliant and offers a little or no resistance to external pressures. Asin the previous constructions, the cell 85 is filled with a referenceliquid 86. The upper end of the soft wall cell is provided with a lowdensity counterbalance cell 87, whereas the lower end of the soft wallcell is provided with a higher density counterbalance cell 88. Either orboth counterbalance cells may be used. The low density counterbalancecell may be filled with a low density liquid, whereas the high densitycounterbalance cell may be filled with liquid or solid material or acombination of both liquid and solid material. Also the counterbalancecells may be formed of solid material of appropriate density. Either orboth counterbalance cells may be used to adjust the net thermalexpansivity or compressibility, or both, of the soft wall hydrometer, todesired values.

The soft wall cell is surrounded by ambient liquid 89, contained withina suitable vessel represented by a wall 90. Secured to the lower end ofthe soft wall cell 85 or to the lower counterbalance cell 88 is aflexible counterbalance link 91, which may be in the form of a chain.The extended end of the link is attached to a traveling nut 92, mountedon an adjustment screw 93, contained within a slotted sleeve 94. Theadjustment screw is rotatable by a screw drive 95. A suitable referencemark 96 is provided on the cell and with the adjustment screw fixed, theelevation of the reference mark may be measured optically. Also thereference mark may be maintained at a constant level and the adjustmentscrew 93 may be moved, the amount of movement being measured bymeasuring movement of the screw drive 95.

Reference is now directed to FIGS. 18 through 20. This constructionlends itself particularly to the laboratory use inasmuch as differentreference liquids may be substituted. This construction utilizes a softwall cell 97 from which extend coaxial integral tubular stems 98.Reference liquid 99 may be drawn into the soft wall cell by immersingone stem in a body of the reference liquid and applying a vacuum to theother stem. One of the stems is closed by a conical pointer tip 100,whereas the other is provided with a seal cap 101, preferably includinga screw thread 102 for attachment to an eyelet 103, or other fulcrummeans. The eyelet 103 may be freely pivoted on a fulcrum post 104. Thehydrometer is immersed in an ambient liquid 105, and an arcuate scale106 is located for cooperation with the pointer 100.

The soft wall cell 97 may be bridged by a counterweight strap 107, whichis provided with a counterweight 108. This simplifies the separationbetween the centers of gravity and of buoyancy that is required for anangular hydrometer of this type. In this connection, it should be notedthat the counterweight may be positive or negative in effect; that is,it may be heavier or lighter than the liquid in which it is immersed.

It should be noted that the cell and stem construction shown in FIGS. 18through 20 may be employed in the types shown in FIGS. 13 through 17.

Reference is now directed to FIG. 21. In this construction, the forceexerted on the hydrometer is opposed by a torsion wire 109, joined atone end to an anchor I and equipped with a dial 111 at its other end, insuch a manner that the wire may be placed under tension and twistedabout its axis. Mounted on the wire is a connector disk 112, to which isattached, intermediate its ends, a lever arm 11,3. One end of the leverarm is provided with a counterweight 114, the other end with a soft wallcell 115. In this case the cell is shown as a cylinder with corrugatedsidewalls, so as to transmit any outside pressure to the referenceliquid contained therein. A pointer 116 and a cooperating scale 117 maybe provided so as to measure the position of the cell when immersed inan ambient liquid.

All of the constructions which have been described have in common a softwall cell which is highly compliant; that is, any external pressure istransmitted to the reference liquid contained within the cell. Thereference liquid may correspond to the ambient liquid, such as in thecase of the first-described structure, in which the reference liquid isa sample of sea water initially at atmospheric pressure. It is notessential in all cases that the reference liquid be a sample veryclosely matched to the ambient liquid. It is advantageous, however, touse a sample closely matched to the ambient liquid, particularly ifextremely high pressures are involved. If a sample, the chemicalcomposition or physical properties of which is closely matched to theambient liquid is used, the effect of pressure on the specific gravityof the ambient liquid is compensated or minimized. I

The highly compliant wall of the hydrometer cell offers no appreciableresistance to the flow of heat into or out of the cell, so that theeffect of temperature is eliminated 'or minimized.

Heretofore, the measurement of the specific gravity of a liquid, exceptby the use of elaborate equipment and very careful thermal and pressurecontrol, has been to an accuracy in the vicinity of 1 part in 1000 or alittle better. By elaborate instrumentation or precautions and extremeenvironmental control, hard wall hydrometer procedures can be pushed toaccuracies many orders of magnitude better. With the use of the softwall hydrometer, corresponding accuracies can be achieved without thestringent demands for environmental control imposed by hard wallprocedures. For example, a 300 cubic centimeter reference volume softwall unit essentially in accordance with FIG. 15 was found to have anaccuracy of approximately 1 part in 100,000 in measurement of sea waterwithout the requirement for precise thermostatic control. The sameaccuracy was attained from an angular system of about 30 cubiccentimeter reference volume essentially equivalent to that of FIG. 20,also without the requirement for precise thermostatic control. The samemeasurements performed with hard wall systems would require extremethermostatic control, to about 001 C. This would be compounded bycorresponding precision in equipment standardization and compensation.

In addition, the soft wall hydrometer enables precision measurementunder pressures which may be so extreme as to preclude measurements byhard'wall procedures. For example, the in situ measurement of oceanicspecific gravity by the apparatus of FIGS. 1 through 12 is intended tobe made at an accuracy of 1 part in 100,000. There are no other presentspecific gravity instruments of corresponding accuracy that may be usedunder pressures attainable in the ocean, nearly 20,000 p.s.i.

It is to be emphasized that all of the described embodiments measure thespecific gravity of the tested fluid, not the density, and that thespecific gravity comparison is --made with the reference fluid and thetested fluid at the same temperature and pressure, where the same meansidentical to the level of accuracy required by the objectives of themeasurement. These embodiments do not measure fluid density because theydo not measure volume and weight directly. They do not measure specificgravity with respect to water or any other reference fluid at a standardtemperature and pressure unless this standard temperature and pressureare among the environmental parameters of the test. The simplest way todescribe the measurement performed by any of the described embodimentsis to describe it as a measurement of relative buoyancy of a referencequantity of a liquid immersed in the liquid to be tested, or theinverse, a measurement of relative buoyancy of a quantity of a liquid tobe tested, immersed in a reference liquid. The critical word isquantity. It is not volume," since this is allowed to vary from thevolume when the cell is initially filled to the volume at the time ofmeasurement, under the influence of temperature and pressure changeswhich occur between the two occasions.

It may seem that this type of measurement preserves buoyant force intransition of a given pair of fluids, one a reference fluid and theother that which 'is to be measured, from a condition of temperature andpressure A to temperature and pressure B, providing the two fluids aresufficiently similar. Similarity is measured by equality of thermalexpansion coefficients and of compressibilities, as modified by theremainder of the assembly, for the two liquids, where equality isdefined by effective equality to the level of accuracy that is desiredfor the specific gravity measurement to be performed.

All of the embodiments described have in common the use of a soft orcompliant cell wall for isolating the reference fluid from the testedfluid and for readily communicating pressure and temperature changesbetween these two liquids. In addition, they all have means foradjustment of the instruments with respect to scale standardization andwith respect to net effective reference compressibility and thermalexpansion coefficient.

Two means of scale standardization are provided in each construction.The first of these is provided by the selection of the reference liquidfor the measurement to be made. The second means for scalestandardization is the adjustability for sensitivity. In the case of theangular systems, sensitivity adjustment is achieved by control of theangle between the cen ters of buoyancy and gravity, measured at the axisof rotation of the hydrometer. As illustrated in FIGS. 1 through 12,this is accomplished by angular adjustment of cell 17 with respect toarm 14, through adjustment screw 16 and bracket 15. In the case oflinear systems, sensitivity adjustment is achieved by design control ofthe rate of change of displacement, or of force, with specific gravity.As illustrated in the chain-opposed construction of FIG. 15, this is afunction of the ratio between nominal volume of the cell 85 and thedisplaced weight per unit length of the chain 91. As illustrated in thedifferential hydrometers of FIGS. 13 and 14, this is a function of thecell volume, stem cross-sectional area and the difference in density ofthe two companion liquids. The other constructions also have easilyrecognizable sensitivity control systems.

The materials suitable for selection for cell walls, structural members,counterweights, and other parts of linear and angular forms of the softwall hydrometer constructions will in general have bulkcompressibilities and thermal expansion coefficients that can differappreciably from those of the reference fluid. For example, acorrosion-resistant steel alloy could be selected as the material to beused for a deep ocean in situ soft wall hydrometer as described in FIGS.1 through 12. The bulk modulus of the alloy may be in the vicinity of 70times that of sea water, and the bulk thermal coefficient may be in thevicinity of one-sixteenth of that of sea water. A possible cell volumewould be 50 cubic centimeters (measured at room temperature andpressure), with a shape as indicated in FIGS. 1 through 12. Let usassume that the SO-cubic-centimeter reference sea water volume requires0.25 cubic centimeters of cell wall to contain it. Let us also assumethat the bracket 15 is designed so as to position its center of gravityon its axis of rotation by the adjustment screw 16, and that thecounterweight 21 has been positioned to align the pointer 22 to thecorrect position on the scale 26 when the hydrometer has beenstandardized by immersion in a sea water of known specific gravity afterthe cell 17 has been angularly positioned with respect to lever 13 toproduce the desired instrumental sensitivity. These standardizingoperations are performed at room temperature at near-zero effectivepressure depth.

Now consider the change that takes place on transport of this assemblyfrom essentially zero-ambient pressure to that at an extreme oceanicdepth, say 15,000 pounds per cubic inch, assuming no change intemperature for the purposes of this calculation. The reference watervolume will be compressed by almost 4 percent, and the volume of themetal in the remainder of the instrument will be compressed aboutoneseventieth as much, or about 0.06 percent. Since the greater fractionof the compression of the reference-water will have taken place bymovement of the opposing cell walls toward one another, and since wehave presumed that one metal was used throughout, the angle between thecenter of the cell and the lever 13, measured around the axis of thejournal shaft 9, will remain constant. The standardizing process hadproduced an angle between the centers of buoyancy and gravity that wouldbe relatively small for an instrument of oceanographic sensitivity.Thus, the position of the center of gravity relative to the lever 13 isessentially unchanged by the pressure. The far greater contributor tothe center of gravity is the cell and its contents, and the center ofthis cell would move inward about 0.06/3==0.02 percent. The remainder ofthe assembly would also be compressed inward by about the same fraction,producing an inward shift of the center of gravity by the samepercentage. The angle between the centers of gravity and of buoyancywill be decreased by approximately the fractional decrease of the cellvolume because of the relatively incompressible metal used in theremainder of the assembly. At the high sensitivities of specific gravityinstruments useful in oceanographic work, the angle between these twocenters is effectively the same as the sine of the angle (when measuredin radians), and the angular specific gravity sensitivity is nearlyinversely proportional to the sine of the angle between the centers.This means that at the extreme pressure of this example and with thisparticular selection of materials, the angular specific gravitysensitivity will be increased by approximately 4 percent. If we considerthe measurement to be made in the open ocean, a representative specificgravity change from top to bottom could be from 1.0000 at the top to1.0023 at the bottom, using the surface ocean water as a reference, adifference of 23 parts per 10,000. This difference includes the effectsof temperature, but this may be ignored for the purposes of thisparticular discussion of materials. If we further desire an accuracy of1 part per 100,000 in specific gravity, this corresponds to a scale thatis at least 230 such parts long, a scale whose sensitivity should remainconstant within a little better than 1 percent for the optimal casewhere the central scale location is halfway between the extremes to bemeasured, at least if scale corrections are not to be applied, or alittle better than 0.5 percent for the case where the central scalelocation is at an extreme. This calls for some form of compensation,either a passive system through design or selection of materials, or anactive system through correction of the measurements that have been madeby use of depth or other data associated with the measurements.

The bracket 15 may be made at least in part of a material whosecompressibility and coefficient of thermal expansion differ from thoseof the reference fluid and the supporting structure, in this wayproviding the opportunity for compensation by preventing sensitivitychange. The objective is to compensate the unbalanced portion of thehydrometer structure with material selected to give it a netcompressibility and ther mal expansion coefficient matched to theambient and reference fluids to the desired level of accuracy. To returnto our example, let us assume that in addition to the 0.25 cubiccentimeters of cell wall, there is an additional and equal volume ofmetal to be compensated from the remainder of the structure. If asuitable plastic material is used as a part of or as a protectivecoating for bracket 15, a relatively small amount can provide therequired compressibility For example, if a silicone rubber whose meancompressibility is 3 times that of sea water is used, approximately 0.2cubic centimeters (at room temperature and pressure) will be sufficient,if it is positioned near the center of gravity of the 0.5 cubiccentimeters of metal to be compensated. The same type of calculation andprocedure may be used for thermal compensation for cases of extremeinstrumental accuracy and reasonably well-known fluids.

The previous discussion has dealt with an angular form of the soft wallhydrometer construction. Essentially the same type of compensation isavailable in the linear forms, again to the desired level of accuracy,by balance between the weights, densities, compressibilities and thermalexpansion coefficients of the structures and counterweights that areidentified in FIGS. 13 through 21. If necessary for extreme accuracy andfor a particular fluid of known behavior, two or more compensatorymaterials may be used to improve the degree of matching and to provide anonlinear compensatory behavior if necessary.

The present embodiments of this invention are to be considered in allrespects as illustrative and not restrictive.

lclaim:

l. A specific gravity sensing instrument, comprising:

a. a closed cell filled with a reference liquid, the wall of said cellbeing highly flexible whereby, when immersed in an ambient liquid, thereference liquid is subjected to the same pressure as the ambientliquid;

b. means for supporting said cell in said ambient liquid for rotationabout a horizontal axis, in response to relative change in density ofthe reference liquid and ambient liquid;

0. means for measuring said rotation;

. means for adjusting said cell on said supporting means to vary thelocation of the center of buoyancy with respect to said axis ofrotation;

e. and a counterweight adjustably mounted on said supporting means tovary the location of the center of gravity with respect to said axis ofrotation.

2. An instrument, as defined in claim 1, wherein said measuring meansincludes:

. an electrode, a confronting-scale element containing a materialsensitive to passage of an electric current, and means for establishinga momentary electric current passing between said electrode and saidscale element to produce an identifying mark on said scale element.

. An instrument, as defined in claim 1, wherein: said cell is attachedto a lever arm pivoted intermediate its ends, and said supporting meansincludes a shaft journaling said lever arm;

. said measuring means include a pointer on said lever arm and a scalepositioned for cooperation with said lever

1. A specific gravity sensing instrument, comprising: a. a closed cellfilled with a reference liquid, the wall of said cell being highlyflexible whereby, when immersed in an ambient liquid, the referenceliquid is subjected to the same pressure as the ambient liquid; b. meansfor supporting said cell in said ambient liquid for rotation about ahorizontal axis, in response to relative change in density of thereference liquid and ambient liquid; c. means for measuring saidrotation; d. means for adjusting said cell on said supporting means tovary the location of the center of buoyancy with respect to said axis ofrotation; e. and a counterweight adjustably mounted on said supportingmeans to vary the location of the center of gravity with respect to saidaxis of rotation.
 2. An instrument, as defined in claim 1, wherein saidmeasuring means includes: a. an electrode, a confronting-scale elementcontaining a material sensitive to passage of an electric current, andmeans for establishing a momentary electric current passing between saidelectrode and said scale element to produce an identifying mark on saidscale element.
 3. An instrument, as defined in claim 1, wherein: a. saidcell is attaChed to a lever arm pivoted intermediate its ends, and saidsupporting means includes a shaft journaling said lever arm; b. saidmeasuring means include a pointer on said lever arm and a scalepositioned for cooperation with said lever arm.
 4. An instrument, asdefined in claim 3, wherein: a. said scale is mounted on a pivotal frameconnected to said shaft independently of said cell-supporting lever arm.5. An instrument, as defined in claim 4, wherein: a. clutch means isprovided to secure said lever arm and pivotal frame to said shaft; b.and means is provided to release said clutch for a predeterminedinterval.